1. Field of the Invention
This invention relates to testing of Semi-Active Laser (SAL) receivers, and more particularly to a SAL beacon that emulates the signature of a SAL designator beam reflected off a target for captive flight-testing of the SAL receiver.
2. Description of the Related Art
Guided Munitions such as missiles, rockets, gun-launched projectiles or bombs may be provided with a fixed or gimballed SAL receiver to detect and track a laser spot to guide the munition to a target. A SAL designator lases the target with an IR laser beam that reflects off the target to form the laser spot. The designator modulates the laser beam with a designation code so that the SAL receiver can discriminate valid and invalid laser spots.
A SAL receiver includes optics to collect and focus the reflected laser energy into a spot on a detector that is responsive to incident energy in the IR spectrum. The detector generates one or more signals that indicate the position of the spot. Most SAL receivers use a quad-cell detector that: outputs sum and difference signals based on measurements from each of the tour cells that indicate the position of the spot. A guidance processor processes these signals to first extract and validate the designation code and then to determine guidance signals based on the position of the spot to guide the munition towards the spot, hence the target.
The design and implementation of the SAL receiver and its host munition must be rigorously tested. An initial rudimentary test is performed in the lab with as simple band-held wand. The wand includes a simple light emitting diode (LED) and modulator that ennui laser beam that is modulated with a designation code. The wand has limited power and must be held up to the SAL receiver. The wand emits a beam that remains stable for only about a few seconds, which is sufficient to verify that the detector is responding, to the IR, beam and to verify the designation code but little else.
To fully test the SAL. receiver and its host munition, the SAL receiver must be excercised over an entire mission from initial target acquisition through launch, tracking and finally end game operations under different tactical and environmental scenarios. These tests are performed on a test. range using an operational SAL designator to illuminate a target and produce a spot that can be acquired a few kilometers away in either a “captive” test in which the munition is mounted on helocopter and flown to emulate the mission without destroying the lased target or a “live fire” test in which the munition is launched, fired, dropped to execute the mission and destroy the target.
For both security and safety reasons, the use of operational SAL designators is tightly controlled. The logistical complexities and cost of performing these tests are high, and not conducive to providing a robust test environment. For example, the designation beam emitted by the SAL designator is not “eye-safe”. This is a major safety concern on test ranges that greatly increases the logistical problems. Also, the SAL designator can only generate a stable designation beam for a limited time period, enough to perform the mission in the field but not optimum to run tests all day long. Because of the logistical issues “captive” tests are only performed on the same day as “live fire” tests.